I’m on the 25th floor of the Trump Tower in New York, sitting opposite Ivanka Trump. She’s a dazzling presence, tall and elegant.At 34, she is the eldest daughter of Donald Trump, the billionaire businessman and would-be president of the US, and his first wife, Ivana, the Czech-American socialite and former model. Ivanka’s skin is luminously moisturised. Her hair, though silky, golden and long, is contained; let’s not forget that in the world of hairstyles, few have had as much impact as her mother’s rock-hard beehive or Donald’s famous swoop-over lift-off. Ivanka looks more like her mother, but she has inherited her father’s superhuman work ethic. She sleeps, she says airily, only“about 4½ hours a night”.

In March this year she gave birth to her third child, Theodore, and only a week later was back on her father’s campaign trail, looking poised and super slim. What happened to the baby belly? What happened to exhaustion hormones? All in check. She said at the time: “As a young girl growing up, my father told me I could do anything that I set my mind to.”And that’s exactly what she did. She was briefly a model, before graduating with an economics degree from Wharton business school in 2004.Along with her two eldest brothers, Ivanka is an executive vice president of development and acquisition at the Trump Organization. She has her own successful fashion brand, and she is writing a book, Women Who Work.

Oh yes, and she and her siblings are increasingly influential in their father’s presidential campaign. Donald, 70, the presumptive Republican nominee for president, is now on his third wife. The real-estate tycoon who helmed the American edition of The Apprentice is taken far more seriously in the US than in Britain, where many see his utterances as unhinged. In America, people look up to the man who is not afraid to say what many think.Trump has five children — three from his first marriage and one each from numbers two and three, the youngest of whom is 10. But it is the elder three who wield the greatest influence over their father’s business ventures and political ambitions.

Ivanka and her brothers Donald Jr, 38, and Eric, 32, are all major players in the Trump presidential campaign, travelling on his campaign plane and sitting with him at his conference table.A few days after we meet, they successfully press him to sack one of his top aides, campaign chairman Corey Lewandowski, who they worried had become a control freak. Reports suggest it was Ivanka who delivered the ultimatum to their father, threatening to distance herself from the campaign if Lewandowski was not removed.

She was right, of course: people were starting to complain that Lewandowski was becoming too abrasive — particularly towards women.At an event in Florida, he was caught on video grabbing a female reporter by the arm. Ivanka is all about taking out the heat, rather than creating it.“Ivanka, Eric and I have the ability to be very candid with our father,” Donald Trump Jr has said. All three children work at Trump Tower, on the floor below their father’s office. He has always involved them just as he was involved himself in his father’s real-estate business, making it an empire, going on to buy ever grander properties. Last week,Trump and his brood were on parade in Scotland boosting their brand at the grand reopening of the Trump Turnberry golf resort, where he hailed Brexit and congratulated Britain on “[taking] their country back”. He attributed the Leave vote chiefly to uncontrolled immigration, and said other countries would follow suit.

When we meet, however, it is clear Ivanka intends to remain above the fray. She is wearing a black and coral floral dress from her own fashion range: V-neck, slightly flared, feminine and in no way overt. Whereas her father thrives on the adrenaline of saying the first thing that comes into his head, Ivanka carefully manicures her thoughts. In person, she’s measured, impressive and athletic-looking.A giant desk separates us. It’s filled with books, notes, her magazine covers and a printed card with what appears to be the Trump manifesto: “We are Determined, Respectful, Engaged,Ambitious, Motivated, Dedicated, Optimistic.” I’m flustered as I grapple for my tape recorder. Ivanka’s voice is soothing as she recommends one of her own handbags with many compartments and a charger for your phone: “It’s coming in the new collection.”

The clothes line is only a small part of what’s occupying her time alongside the Trump campaign, the family’s real-estate deals and, of course, her three kids. She tells me she’s always literally running home to check on them.There’s a camera linked to the office, too, so she knows what they are up to. Ivanka recently tweeted that baby Theodore has started sleeping through the night at two months. How did she manage to get him to do that?

“With each child we got them on a sleep schedule in a quicker fashion,” she says.“However,Arabella [her oldest daughter, aged 4] was a disaster because we didn’t know what we were doing and it took a year. Joseph [aged 2] was half that, but with Theodore we’re learning how to do it.”

Her husband, Jared Kushner, is also involved with Trump’s campaign. He is another American businessman — the publisher of The New York Observer and heads his family’s real-estate development company, Kushner Companies.They married in 2009 after she converted to Judaism for him.“I’m incredibly in love with him and he’s my best friend,” she says. He was raised Orthodox. She is observant of the Sabbath and has even learnt to cook kosher.“I was a terrible cook. I’ve always loved entertaining and having people in my home but I would normally order food.When I got married I decided that was something I would learn how to do,” she says.

As well as an apartment in Manhattan (on the Upper East Side) they have a cottage at one of the Trump golf clubs in New Jersey, next to her father’s. She and her family escape there at weekends. How is Donald as a grandfather? “Excellent, excellent. My kids love him and we spend a lot of time together, especially during the summer. It’s very cute that my daughter has picked up little things from him. A couple of months ago we were walking down the street in New York City and she spotted a pothole in the road. She points at me and looks at it and says,‘Mom, Grandpa would not like that.’

We laugh and then she goes,‘You know, that sort of meticulousness that he has.’ He is incredibly close with my children.”Her eyes light up when she’s talking about her dad. “My father has tremendous warmth,” she continues. “He is a fiercely loyal person to his family and friends. He has an amazing — and albeit sometimes wicked — sense of humour. He has been an unbelievable father to me and my siblings.” Trump is a man who doesn’t think before he speaks and doesn’t realise that his “jokes” can often be taken out of context — and she hasn’t always been shielded from them herself. A former Miss Universe contestant recalled the time Donald called his own daughter“hot”, asking: “Don’t you think my daughter’s hot? She’s hot, right?” Ivanka was 16 at the time. Does she think his sense of humour has been taken in the wrong way? “Potentially,” she says cautiously. Perhaps he shouldn’t joke so much in public, I suggest. Ivanka demurs, as she does about all his controversial politicking. Rather than try and defend his divisive views, she says: “He is also authentic.A component of his success has been that people respect the fact that he’s incredibly honest with his opinions, and in politics that’s remarkably rare, if not unheard of. So I think that’s a refreshing quality. Regardless of whether people agree or disagree with a certain political stance, I do think there’s an appreciation that he is not afraid to say where he stands on a given issue.”

So,Team Trump.Would she, could she, be a running mate? It has been suggested she would be his perfect foil.“Oh gosh, he’s keeping me busy here at Trump. I also have my own business and a young family. Quite a few things on my plate and I’m very happy.” It’s not exactly a denial. Of course, everyone has been asking me: what does she think about Trump’s plans to build a wall to keep out the Mexicans, and banning Muslims from entering the US? What does she think about profiling? But of course she’s not going to tell me — those questions are off limits. She sails on unruffled, super-controlled, immune to his turbulence.The best I can do is ask her how things would change if she was to get the title First Daughter? “You’ll have to ask me in a year from now. I’m trying not to think too far ahead of myself. I’m an adult now, so obviously it would be a different experience

than if I were a child. But I’m still a daughter.” I read that she was close friends with the former First Daughter Chelsea Clinton.“Yes, we’ve known each other for years and she’s a wonderful person and a very good friend.” So despite their parents running against each other, their friendship remains. Ivanka is very much a feminist.“I 100% believe in gender equality so by definition that makes me a feminist, which I’m very proud of.” Surprisingly, she also thinks her father is a feminist — despite many accusations against him of misogyny, objectifying women and generally cussing them out (but who does he not cuss out?).“I do, yes and it’s a big reason I am the woman I am today. He always told me and showed me that I could do anything I set my mind to if I married vision and passion with work ethic. He’s also surrounded me with strong female role models who have done just that since I was a little girl. People talk about gender equality. He has lived it, he has employed women at the highest levels of the Trump Organization for decades, so I think it’s a great testament to how capable he thinks women are and has shown that his whole life.” I think she’s always been a daddy’s girl. She used to watch Donald in the office and on construction sites when she was little, just to observe his process. She becomes a little more hesitant at this; you can see her choosing words carefully.“Yes I did. I think there’s a genetic component as well as an experiential component to my love for real estate. Both my parents really loved what they did professionally and shared their passion with us starting from a young age. It’s no coincidence that my brothers and I like showing up for work.That’s what they modelled for us.”

“But they didn’t force it upon us,” she adds.“The number one thing my father said to me my whole life was that you need to find what you’re passionate about, because life is too short to do something you don’t love and if you are not passionate you will never be great.And I’ve noticed that to be true. People who are the most successful are the most passionate. It’s much easier to cut corners if you care less deeply.”

Born and raised in New York, she was a straight-A student and responsible for earning her own spending money, which is why she took up modelling in her teens. In her book The Trump Card, she wrote: “It’s as ruthless an industry as real estate… models were the meanest, cattiest, bitchiest girls on the planet. Entitled, unsupervised, under educated and pampered teenagers whose every success came as the direct result of someone else’s disappointment.” She got out of that fast,went to university and worked for other companies before joining Trump.

She’s not someone who thinks that famous parents are a curse — despite what she went through when her parents,who were very much the New York power couple, divorced in 1992. She learnt all about her father’s mistress, the actress Marla Maples,who became his second wife. Reporters would ask her about her father’s sexual prowess and she was hounded by paparazzi.

Yet, the Trump name is, she says,“a tremendous blessing. I look at the great fortune I’ve had my entire life.There are people starving around the globe. Some people think having a successful or famous parent can be paralysing in that they feel they could never live up to what was accomplished by the generation before them.The flip side is that it can be a great motivator if you harness that energy and use it productively.”

She’s close to both her parents and said in the past that the divorce “brought me closer to my father, not because I was taking his side but because I could no longer take him for granted”. So she supported him, a week after giving birth, on that podium in New York. Was that not hard? “I try to live my life in accordance with my priorities. My family is always my first priority.”

She believes her attitude to raising children is very different from that of her mother’s generation.“There used to be a work life and a home life. Now there is one life,” she says.“No one I know has a work wardrobe any more, or an area of their closet that’s designated for work.We transition through roles more fluidly.

Technology has been a huge enabler of that because it became normal to respond to work emails at 11 o’clock at night and therefore permissible to pick up the phone when your child was calling at the end of the school day.” She adds: “I don’t do it all myself. I’m very fortunate to have childcare to help me while I am at work.” In fact, she rejects “the concept of ‘having it all’ because that’s the wrong way to look at things. It implies there’s one definition for personal and another for professional success and I don’t believe that to be true.And I think people are trying to cast women as uniform and one-dimensional.A better way to look at it is, you are the architect of your own life and you have to live in accordance with the things you prioritise.”

She has recently started to enjoy running.“I absolutely hated it, then my team here and I trained for a half marathon in Central Park. Now I run with my husband on Saturday mornings. I’m probably the only person who runs without music, without a phone. It’s just great to be able to talk to him.”

Every year, she and Kushner like to go to Turnberry, which she says “is without doubt the greatest golf resort in the world”. She thinks the only way to reallyget to know someone is during four hours on a golf course. She claims not to be a “particularly good” golfer, though I doubt there’s much in her life that she’s not exemplary at. She disagrees, and worries that I might think she’s too perfect.“You know, I get very messy. I don’t want to project an image that everything is simple and easy, because that’s not helpful to women, because raising children is really tiring and exhausting. I sleep very little, and I don’t advocate that, but there are things that I want to accomplish. I will leave the office early to have dinner with my kids, put them to bed and get back to work rather late. It’s a choice that I feel good about. I’m OK about losing a little bit of sleep to create a schedule that works for my life.” “I’m also of my generation,” she says,“a millennial woman who is ambitious. I have a lot of things to accomplish professionally.And I swing for the fences.” What does that mean? “It’s a baseball expression. It means I dream big.” And live big? “No I don’t. I don’t live to excess.”

Indeed. Everything about her mindset and physical appearance is contained, balanced, the antithesis of her father. I like her, but I still don’t feel I know who she really is. I put it in another way: if she were a shoe, what kind would she be? “Oh, I would be my Carra pump from my own range.” She takes off her coral-coloured stiletto and shows it to me for inspection.“It’s my go-to. Remarkably comfortable, but I could run a marathon in these.” But that heel is four or five inches high.“They’re comfortable. I would never wear a shoe that would require me to teeter around.” Mystery still unsolved.A woman in 4½in stilettos can only run a marathon if she’s Ivanka Trump.